An inflator assembly for inflating an inflatable vehicle occupant restraint, such as an air bag, may include a pressure vessel which stores gas for inflating the restraint. Such an inflator assembly is disclosed in co-pending U.S. patent application Ser. No. 761,685, filed Sep. 18, 1991, now abandoned, entitled "Apparatus for Inflating a Vehicle Occupant Restraint," and assigned to TRW Vehicle Safety Systems Inc. The inflator assembly disclosed in that co-pending patent application includes a pressure vessel which contains a combustible mixture of gases. The inflator assembly is actuated to inflate the vehicle occupant restraint in response to vehicle deceleration of a magnitude which indicates the occurrence of a collision. When the inflator assembly is thus actuated, the combustible mixture of gases in the pressure vessel is ignited. The gas pressure inside the pressure vessel is then increased by the heat which results from the combustion of the mixture of gases. When the increasing gas pressure reaches a predetermined elevated level, it ruptures a burst disk to open the pressure vessel. The vehicle occupant restraint is then inflated by gas which flows outward from the pressure vessel and into the vehicle occupant restraint at an elevated pressure level.